Duplicate DNS entries

I have duplicate DNS entries on my server (two machines with the same DNS given out by the server).  Generally one DNS entry is several months old and the other is newer.  How do I correct this other than just deleting the older one?  How do I prevent this from happening again?
David ImbrognoAsked:
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Paul MacDonaldDirector, Information SystemsCommented:
Do you have two machines with the same IP address, or do you have one machine with two IP addresses?

In the first case, are both machines DHCP clients?  Only one?  Neither?

In the second case, is the machine a DHCP client?

What is your DHCP scope?
DrDave242Senior Support EngineerCommented:
How do I prevent this from happening again?

DNS scavenging may be just what you're looking for. It periodically scans your DNS zones for stale records (records that haven't been refreshed or updated in a while) and deletes them. Bad things can happen (valid records being deleted, for example) if it's not configured correctly, though, so I highly recommend reading this article carefully before enabling it:

https://blogs.technet.microsoft.com/networking/2008/03/19/dont-be-afraid-of-dns-scavenging-just-be-patient/

Yes, it's almost ten years old, but it's still relevant.

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David ImbrognoAuthor Commented:
Two machines have the same IP address.  Both assigned by DHCP.  DHCP scope is 10.10.248.1 through 10.10.253.254
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Paul MacDonaldDirector, Information SystemsCommented:
And you only have one DHCP server?  And only one scope?
David ImbrognoAuthor Commented:
Yes  Only one DHCP server and one scope.  I do have two DNS servers however
DrDave242Senior Support EngineerCommented:
Two machines have the same IP address.  Both assigned by DHCP.

This is a separate issue from the one in your original question. DNS records that are inaccurate because they're several months out of date can be fixed by scavenging, but this is a DHCP problem. Please run ipconfig /all on both of those machines and confirm whether they were both assigned by the same DHCP server and have overlapping lease times.
David ImbrognoAuthor Commented:
The machines appear to have had the IP addresses assigned by the same DHCP server and they do have overlapping lease times
DrDave242Senior Support EngineerCommented:
I have no idea how that could happen. Once a DHCP server has leased an address to a client, it should never lease that same address to another client while the original lease is still active; that's one of the core principles of DHCP. Do both leases show up in the DHCP console?

Is your DHCP server a Windows server, BTW, or something else?
Paul MacDonaldDirector, Information SystemsCommented:
Yeah, this shouldn't happen with Windows DHCP.  Moreover, if there were another DHCP server on your network (a lot of home/small business routers also do DHCP), I would expect you'd have many more problems than just this one computer.  Very odd.  Still worth looking for another DHCP server on the network though.
David ImbrognoAuthor Commented:
Thank you for the help.  I will set up DNS scavenging and see what happens.
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